Expert: Tom Whiting - 6/7/2006

Question
I recently went on a cruise in the Caribbean.  While walking on the deck one night, I noticed that I did not see the moon.  I thought that it might have been a cloudy night.  Therefore, I checked again the next night and didn't see anything.  Even if it had been a cloudy night, shouldn't I have seen some kind of light?  Can you explain why we couldn't see it?

Answer
Hi Jamie,
Yes, easy answer.  The moon, just like the sun, or any other
star......for most of the world, except the extreme polar regions.....is above an observer's horizon for about 12 hours, and below your horizon for 12 hours.

That is, for about half the day we face the sun  (and/or the moon, or any other heavenly body) and for half the day, we don't....face it.
Perhaps you were on your cruise on the weekend of May
25-28....if so, the moon was new phase, thus very close to
the sun and not illuminated at all (except for the back side
which we can't ever see).  Or, perhaps you were on your
cruise from May 19 until May 24, in which case the moon
phase was last quarter and waning (early morning) crescent
phase, which means it didn't rise until 1-3 am...maybe you
had retired to bed before the moon rose in the east.
(If you could furnish me the exact dates of your cruise, with my Skyglobe program, I could tell you exactly when you had moonrise and moonset from anywhere in the world- and the phase angle).

(A last quarter moon would rise around 2 am EDT in the
east and set around 2 pm in the west....did you remember
to check the 9 am daytime sky in the South or southwest
for a daytime moon?  It would have been visible in a clear,
blue sky. )

Actually, astronomy-wise, you had the best times to be
on vacation....we experienced astronomers actually hate
the moon, as it's just another light polluter.  We only go
out to observe on the weekend of new moon to observe
the deep sky objects --  the moon washes out all the deep
sky objects like the Andromeda Galaxy, ring nebula, Stephen's Quintet, and millions of other objects. The only
observers that go out with a moon out, are the lunar/planetary observers and the double star observers, as the moon (and artificial light pollution) does not hurt them.
But it kills off the intensity of the deep sky objects.
Well, hope all this helps, and I'll be waiting to hear your
cruise dates...in fact, if you wish, E-mail them to me directly
and I will give you your exact moonrise/moonset times for
those dates, at
bwhiting@velocity.net

And check out my newly built 30 inch portable telescope on
our club website at
http://www.velocity.net/~bwhiting
and punch on the 30 inch scope pictures.
 
Hope all this helps,
Clear Skies,
Tom Whiting     Pres. ECMOG
Erie, PA.